Mold-cooling temperature

Time, pressure, and temperature controls indicate whether the performance requirements of a molded product are being met. The time factors include the rate of injection, duration of ram pressure, time of cooling, time of piastication, and screw RPM. Pressure requirement factors relate to injection high and low pressure cycles, back pressure on the extruder screw, and pressure loss before the plastic enters the cavity which can be caused by a variety of restrictions in the mold. The temperature control factors are in the mold (cavity and core), barrel, and nozzle, as well as the melt temperature from back pressure, screw speed, frictional heat, and so on in the plasticator. 

The results of calculations for two values of the initial temperature of the reactive mass To are shown in Fig. 4.17. For To = 70°C, the curves are practically insensitive to the value of to. This is explained by the fact that the mold temperature is lower than the initial temperature of the reactive mass (polyurethane composition) and therefore the layers of polymeric material close to the surface of the mold cool rapidly down to the temperature Ts, because this temperature is strictly constant. 

Fig. 43. Effect of cooling temperature from molding temperature on the bending moment-displacement curves of a notched PA 6 sample...

Prevention and Control Cool temperatures and high humidity promote Botrytis fruit rot. Removing infected fruit, whether living or dead, reduces the spread of the disease. Plants overstimulated with nitrogen fertilizer are most susceptible to gray mold, as are plants around which air cannot circulate to quickly dry leaves, stems, and fruit. 

The important variables of transfer molding are the polymer type, melt temperature, pot hold time, transfer pressure, transfer rate, hold-up time in the filled mold, and the mold cooling. These variables are briefly reviewed in this section. 

Tempering - Homogeneous tempering refers to minimization of the mold surface temperature between the inlet and outlet of the cooling fluid. 

It wonld be illusory to expect to avoid these serious problems by completely eliminating the microorganisms involved. Indeed, there are a number of very moldy cellars where wine ages perfectly well. Of course, it is nevertheless advisable to restrict mold populations by keeping premises clean and controlling humidity, as weU as ensuring adequate ventilation and cool temperatures. The most important recommendation is to prohibit the use of chlorine derivatives as fungicides. 

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